1. Field of the Invention
The present invention relates to a cap of a fuel tank with a pressure control valve for controlling pressure in the fuel tank.
2. Description of the Related Art
One known example of fuel tank caps is disclosed in JAPANESE UTILITY PATENT PUBLICATION GAZETTE No. 6-88606. FIG. 38 is a sectional view illustrating a fuel tank cap 300. As shown in FIG. 38, the fuel tank cap 300 includes a plastic casing body 302 screwed to a filler neck FN of a fuel tank (not shown), a cover member 330 attached to the casing body 302, and a negative pressure valve 340 received in a valve chamber 304 of the casing body 302 for controlling pressure in the fuel tank. The negative pressure valve 340 includes a rubber valve body 342, a valve supporting member 346 with a fitting aperture 346a for supporting the valve body 342, and a spring 348 for pressing the valve body 342. When the differential pressure between the tank pressure and the atmospheric pressure applied to the valve body 342 increases to or above a predetermined level, the negative pressure valve 340 opens to make the tank pressure approach atmospheric pressure.
Flange members 308 extending outward in the radial direction of the casing body 302 are formed above the casing body 302. The flange members 308 are fitted in the cover member 330 and thereby support the cover member 330. Each flange member 308 has a fragile portion D. The fragile portion D has a plurality of V grooves Da and Db concentrically formed in an upper surface and a lower surface of the flange member 308. In the state that the fuel tank cap 300 is screwed to the filler neck FN, when an external force is applied to the fragile portion D via the cover member 330, for example, by a body outer plate (not shown), the fragile portion D is broken on a line connecting the V groove Da with the V groove Db. This separates the flange members 308 from the casing body 302 and thereby ensures the sealing property of the filler neck FN.
Since the fragile portions D are formed concentrically in the flange members 308 that extend outward in the radial direction of the casing body 302, there is a distribution of the breaking load according to the direction of external forces.